xref: /openbmc/linux/drivers/mtd/spi-nor/otp.c (revision 388161ca)

// SPDX-License-Identifier: GPL-2.0
/*
 * OTP support for SPI NOR flashes
 *
 * Copyright (C) 2021 Michael Walle <michael@walle.cc>
 */

#include <linux/log2.h>
#include <linux/mtd/mtd.h>
#include <linux/mtd/spi-nor.h>

#include "core.h"

#define spi_nor_otp_region_len(nor) ((nor)->params->otp.org->len)
#define spi_nor_otp_n_regions(nor) ((nor)->params->otp.org->n_regions)

/**
 * spi_nor_otp_read_secr() - read security register
 * @nor:	pointer to 'struct spi_nor'
 * @addr:       offset to read from
 * @len:        number of bytes to read
 * @buf:        pointer to dst buffer
 *
 * Read a security register by using the SPINOR_OP_RSECR commands.
 *
 * In Winbond/GigaDevice datasheets the term "security register" stands for
 * an one-time-programmable memory area, consisting of multiple bytes (usually
 * 256). Thus one "security register" maps to one OTP region.
 *
 * This method is used on GigaDevice and Winbond flashes.
 *
 * Please note, the read must not span multiple registers.
 *
 * Return: number of bytes read successfully, -errno otherwise
 */
int spi_nor_otp_read_secr(struct spi_nor *nor, loff_t addr, size_t len, u8 *buf)
{
	u8 addr_width, read_opcode, read_dummy;
	struct spi_mem_dirmap_desc *rdesc;
	enum spi_nor_protocol read_proto;
	int ret;

	read_opcode = nor->read_opcode;
	addr_width = nor->addr_width;
	read_dummy = nor->read_dummy;
	read_proto = nor->read_proto;
	rdesc = nor->dirmap.rdesc;

	nor->read_opcode = SPINOR_OP_RSECR;
	nor->read_dummy = 8;
	nor->read_proto = SNOR_PROTO_1_1_1;
	nor->dirmap.rdesc = NULL;

	ret = spi_nor_read_data(nor, addr, len, buf);

	nor->read_opcode = read_opcode;
	nor->addr_width = addr_width;
	nor->read_dummy = read_dummy;
	nor->read_proto = read_proto;
	nor->dirmap.rdesc = rdesc;

	return ret;
}

/**
 * spi_nor_otp_write_secr() - write security register
 * @nor:        pointer to 'struct spi_nor'
 * @addr:       offset to write to
 * @len:        number of bytes to write
 * @buf:        pointer to src buffer
 *
 * Write a security register by using the SPINOR_OP_PSECR commands.
 *
 * For more information on the term "security register", see the documentation
 * of spi_nor_otp_read_secr().
 *
 * This method is used on GigaDevice and Winbond flashes.
 *
 * Please note, the write must not span multiple registers.
 *
 * Return: number of bytes written successfully, -errno otherwise
 */
int spi_nor_otp_write_secr(struct spi_nor *nor, loff_t addr, size_t len,
			   const u8 *buf)
{
	enum spi_nor_protocol write_proto;
	struct spi_mem_dirmap_desc *wdesc;
	u8 addr_width, program_opcode;
	int ret, written;

	program_opcode = nor->program_opcode;
	addr_width = nor->addr_width;
	write_proto = nor->write_proto;
	wdesc = nor->dirmap.wdesc;

	nor->program_opcode = SPINOR_OP_PSECR;
	nor->write_proto = SNOR_PROTO_1_1_1;
	nor->dirmap.wdesc = NULL;

	/*
	 * We only support a write to one single page. For now all winbond
	 * flashes only have one page per security register.
	 */
	ret = spi_nor_write_enable(nor);
	if (ret)
		goto out;

	written = spi_nor_write_data(nor, addr, len, buf);
	if (written < 0)
		goto out;

	ret = spi_nor_wait_till_ready(nor);

out:
	nor->program_opcode = program_opcode;
	nor->addr_width = addr_width;
	nor->write_proto = write_proto;
	nor->dirmap.wdesc = wdesc;

	return ret ?: written;
}

static int spi_nor_otp_lock_bit_cr(unsigned int region)
{
	static const int lock_bits[] = { SR2_LB1, SR2_LB2, SR2_LB3 };

	if (region >= ARRAY_SIZE(lock_bits))
		return -EINVAL;

	return lock_bits[region];
}

/**
 * spi_nor_otp_lock_sr2() - lock the OTP region
 * @nor:        pointer to 'struct spi_nor'
 * @region:     OTP region
 *
 * Lock the OTP region by writing the status register-2. This method is used on
 * GigaDevice and Winbond flashes.
 *
 * Return: 0 on success, -errno otherwise.
 */
int spi_nor_otp_lock_sr2(struct spi_nor *nor, unsigned int region)
{
	u8 *cr = nor->bouncebuf;
	int ret, lock_bit;

	lock_bit = spi_nor_otp_lock_bit_cr(region);
	if (lock_bit < 0)
		return lock_bit;

	ret = spi_nor_read_cr(nor, cr);
	if (ret)
		return ret;

	/* no need to write the register if region is already locked */
	if (cr[0] & lock_bit)
		return 0;

	cr[0] |= lock_bit;

	return spi_nor_write_16bit_cr_and_check(nor, cr[0]);
}

/**
 * spi_nor_otp_is_locked_sr2() - get the OTP region lock status
 * @nor:        pointer to 'struct spi_nor'
 * @region:     OTP region
 *
 * Retrieve the OTP region lock bit by reading the status register-2. This
 * method is used on GigaDevice and Winbond flashes.
 *
 * Return: 0 on success, -errno otherwise.
 */
int spi_nor_otp_is_locked_sr2(struct spi_nor *nor, unsigned int region)
{
	u8 *cr = nor->bouncebuf;
	int ret, lock_bit;

	lock_bit = spi_nor_otp_lock_bit_cr(region);
	if (lock_bit < 0)
		return lock_bit;

	ret = spi_nor_read_cr(nor, cr);
	if (ret)
		return ret;

	return cr[0] & lock_bit;
}

static loff_t spi_nor_otp_region_start(const struct spi_nor *nor, unsigned int region)
{
	const struct spi_nor_otp_organization *org = nor->params->otp.org;

	return org->base + region * org->offset;
}

static size_t spi_nor_otp_size(struct spi_nor *nor)
{
	return spi_nor_otp_n_regions(nor) * spi_nor_otp_region_len(nor);
}

/* Translate the file offsets from and to OTP regions. */
static loff_t spi_nor_otp_region_to_offset(struct spi_nor *nor, unsigned int region)
{
	return region * spi_nor_otp_region_len(nor);
}

static unsigned int spi_nor_otp_offset_to_region(struct spi_nor *nor, loff_t ofs)
{
	return div64_u64(ofs, spi_nor_otp_region_len(nor));
}

static int spi_nor_mtd_otp_info(struct mtd_info *mtd, size_t len,
				size_t *retlen, struct otp_info *buf)
{
	struct spi_nor *nor = mtd_to_spi_nor(mtd);
	const struct spi_nor_otp_ops *ops = nor->params->otp.ops;
	unsigned int n_regions = spi_nor_otp_n_regions(nor);
	unsigned int i;
	int ret, locked;

	if (len < n_regions * sizeof(*buf))
		return -ENOSPC;

	ret = spi_nor_lock_and_prep(nor);
	if (ret)
		return ret;

	for (i = 0; i < n_regions; i++) {
		buf->start = spi_nor_otp_region_to_offset(nor, i);
		buf->length = spi_nor_otp_region_len(nor);

		locked = ops->is_locked(nor, i);
		if (locked < 0) {
			ret = locked;
			goto out;
		}

		buf->locked = !!locked;
		buf++;
	}

	*retlen = n_regions * sizeof(*buf);

out:
	spi_nor_unlock_and_unprep(nor);

	return ret;
}

static int spi_nor_mtd_otp_range_is_locked(struct spi_nor *nor, loff_t ofs,
					   size_t len)
{
	const struct spi_nor_otp_ops *ops = nor->params->otp.ops;
	unsigned int region;
	int locked;

	/*
	 * If any of the affected OTP regions are locked the entire range is
	 * considered locked.
	 */
	for (region = spi_nor_otp_offset_to_region(nor, ofs);
	     region <= spi_nor_otp_offset_to_region(nor, ofs + len - 1);
	     region++) {
		locked = ops->is_locked(nor, region);
		/* take the branch it is locked or in case of an error */
		if (locked)
			return locked;
	}

	return 0;
}

static int spi_nor_mtd_otp_read_write(struct mtd_info *mtd, loff_t ofs,
				      size_t total_len, size_t *retlen,
				      const u8 *buf, bool is_write)
{
	struct spi_nor *nor = mtd_to_spi_nor(mtd);
	const struct spi_nor_otp_ops *ops = nor->params->otp.ops;
	const size_t rlen = spi_nor_otp_region_len(nor);
	loff_t rstart, rofs;
	unsigned int region;
	size_t len;
	int ret;

	if (ofs < 0 || ofs >= spi_nor_otp_size(nor))
		return 0;

	/* don't access beyond the end */
	total_len = min_t(size_t, total_len, spi_nor_otp_size(nor) - ofs);

	if (!total_len)
		return 0;

	ret = spi_nor_lock_and_prep(nor);
	if (ret)
		return ret;

	if (is_write) {
		ret = spi_nor_mtd_otp_range_is_locked(nor, ofs, total_len);
		if (ret < 0) {
			goto out;
		} else if (ret) {
			ret = -EROFS;
			goto out;
		}
	}

	while (total_len) {
		/*
		 * The OTP regions are mapped into a contiguous area starting
		 * at 0 as expected by the MTD layer. This will map the MTD
		 * file offsets to the address of an OTP region as used in the
		 * actual SPI commands.
		 */
		region = spi_nor_otp_offset_to_region(nor, ofs);
		rstart = spi_nor_otp_region_start(nor, region);

		/*
		 * The size of a OTP region is expected to be a power of two,
		 * thus we can just mask the lower bits and get the offset into
		 * a region.
		 */
		rofs = ofs & (rlen - 1);

		/* don't access beyond one OTP region */
		len = min_t(size_t, total_len, rlen - rofs);

		if (is_write)
			ret = ops->write(nor, rstart + rofs, len, buf);
		else
			ret = ops->read(nor, rstart + rofs, len, (u8 *)buf);
		if (ret == 0)
			ret = -EIO;
		if (ret < 0)
			goto out;

		*retlen += ret;
		ofs += ret;
		buf += ret;
		total_len -= ret;
	}
	ret = 0;

out:
	spi_nor_unlock_and_unprep(nor);
	return ret;
}

static int spi_nor_mtd_otp_read(struct mtd_info *mtd, loff_t from, size_t len,
				size_t *retlen, u8 *buf)
{
	return spi_nor_mtd_otp_read_write(mtd, from, len, retlen, buf, false);
}

static int spi_nor_mtd_otp_write(struct mtd_info *mtd, loff_t to, size_t len,
				 size_t *retlen, const u8 *buf)
{
	return spi_nor_mtd_otp_read_write(mtd, to, len, retlen, buf, true);
}

static int spi_nor_mtd_otp_lock(struct mtd_info *mtd, loff_t from, size_t len)
{
	struct spi_nor *nor = mtd_to_spi_nor(mtd);
	const struct spi_nor_otp_ops *ops = nor->params->otp.ops;
	const size_t rlen = spi_nor_otp_region_len(nor);
	unsigned int region;
	int ret;

	if (from < 0 || (from + len) > spi_nor_otp_size(nor))
		return -EINVAL;

	/* the user has to explicitly ask for whole regions */
	if (!IS_ALIGNED(len, rlen) || !IS_ALIGNED(from, rlen))
		return -EINVAL;

	ret = spi_nor_lock_and_prep(nor);
	if (ret)
		return ret;

	while (len) {
		region = spi_nor_otp_offset_to_region(nor, from);
		ret = ops->lock(nor, region);
		if (ret)
			goto out;

		len -= rlen;
		from += rlen;
	}

out:
	spi_nor_unlock_and_unprep(nor);

	return ret;
}

void spi_nor_otp_init(struct spi_nor *nor)
{
	struct mtd_info *mtd = &nor->mtd;

	if (!nor->params->otp.ops)
		return;

	if (WARN_ON(!is_power_of_2(spi_nor_otp_region_len(nor))))
		return;

	/*
	 * We only support user_prot callbacks (yet).
	 *
	 * Some SPI NOR flashes like Macronix ones can be ordered in two
	 * different variants. One with a factory locked OTP area and one where
	 * it is left to the user to write to it. The factory locked OTP is
	 * usually preprogrammed with an "electrical serial number". We don't
	 * support these for now.
	 */
	mtd->_get_user_prot_info = spi_nor_mtd_otp_info;
	mtd->_read_user_prot_reg = spi_nor_mtd_otp_read;
	mtd->_write_user_prot_reg = spi_nor_mtd_otp_write;
	mtd->_lock_user_prot_reg = spi_nor_mtd_otp_lock;
}